1. Field of the Invention
The present invention relates to an ink film cassette internally accommodating an ink film used by thermal transfer recording devices.
2. Description of the Related Art
Thermal transfer recording devices are provided with a platen roller and a thermal head which can be brought into pressure contact and released from pressure contact with said platen roller, and feed a recording sheet between the platen roller and the thermal head. An ink film, the surface of which on one side is coated with heat fusion characteristics or thermal sublimation characteristics, is transported between the recording sheet and the thermal head. The ink film is fed out from a supply reel, and taken up on a take-up reel. When a color image is reproduced on a recording sheet by a single thermal head, the ink film used has a thin film base surface coated sequentially by yellow, magenta, and cyan color inks.
In thermal transfer recording devices of recent years, ink film cassettes are used which house a supply reel and a take-up reel and which are removably loaded in the body of the thermal transfer recording device so as to improve the operation of loading the ink film. Ink film cassettes are consumable components, which are replaced by a new cassette when the ink film accommodated therein has been used.
During printing, the ink film is pulled out from the supply reel and transported together with the movement of the recording sheet via the friction force with the recording sheet being transported between the platen roller and the thermal head disposed in a state of pressure contact relative to said platen roller. On the other hand, the ink film that has been fed from the supply reel is rolled up on the take-up reel via the rotation of the take-up reel rotated by a motor provided within the body of the thermal transfer recording device.
A supply torque limiter is provided within the body of the thermal transfer recording device and is connected to the supply reel when the ink film cassette is installed so as to apply a damping force on the supply reel. Tension is applied to the ink film during printing by feeding the ink film as a breaking force is applied to the supply reel by the supply torque limiter so as to prevent the ink film from wrinkling.
A take-up torque limiter for limiting the drive torque of the take-up reel is provided between the take-up reel and the motor in the body of the thermal transfer recording device. The take-up torque limiter exerts tension on the ink film during printing as previously described, and is also provided for the reasons described below. That is, although the moving speed of the recording sheet and the moving speed of the ink film must be identical during printing, the ink film take-up speed changes in conjunction with the change in the take-up diameter even though the shaft of the take-up reel is rotated at uniform speed. The take-up torque limiter is provided so that the take-up speed follows the ink film moving speed during printing to wind the ink film on the take-up reel without slack.
In conventional ink film cassettes, the supply reel and take-up reel are housed within the cassette so as to be smoothly rotated. That is, the oscillation resistance between the shaft of the supply reel and the cassette supporting said shaft, and the oscillation resistance between the shaft of the take-up reel and the cassette supporting said shaft are minimized.
During transport and delivery of the consumable ink film cassette, the ink film is easily fed from the supply reel via the application of an external force because a rotational load is not exerted on the supply reel within the cassette. Thus, a portion of the unused ink film becomes wrinkled, and needlessly rendered unusable.
Among the various used forms of ink film cassette is a typical form wherein a cassette is removed from the apparatus body before the ink film accommodated within a single cassette is completely used, then the same cassette is again reinstalled in the apparatus. In this instance, the action of an external force while the ink cassette is removed readily causes the ink film to be fed out from the supply reel and needlessly renders the ink film unusable as previously described.
Furthermore, since rotational load is not exerted on the take-up reel within the cassette when the ink film cassette is removed from the apparatus body, the application of an external force can readily cause the spent ink film to loosen and be fed out from the take-up roller, allowing possible damage to the ink film.
When the ink film becomes slack, the loose film rewinds back on the supply reel when the cassette is installed, such that an operation is required to rewind the film back on the take-up reel, thereby complicating the procedure of installation.
In order to prevent the unused film from feeding out from the supply reel and the used film from feeding out from the take-up reel, a stopper must be provided on the shaft of each reel to prevent rotation of the supply reel and take-up reel, thereby markedly complicating operation of the cassette.
Because a supply torque limiter and take-up torque limiter are provided within the body of the thermal transfer recording device, the construction of the apparatus is complicated, the cost of the device is increased, and the compact design of the device is prevented.
The torque limiters provided within the device must have durability comparable to that of other components in the device, for example, durability adequate for normally forming 60,000 images. Thus, relatively expensive torque limiters must be used, thereby increasing the cost of the component as well as the total cost of the thermal transfer recording device.
In the thermal transfer recording device, when the thermal head changes from the non-contact state to the contact state relative to the platen roller, the ink film is slightly rolled up on the take-up reel to eliminate the slack in the film. Thus, in ink film used for color printing, the regions coated with the color inks are larger relative to the print region in consideration of unused film which is slightly fed out from the supply reel. One requirement of the ink film cassette is to economize on the ink or ink film by reducing the region of the color inks.
There is a need for an ink film cassette capable of automatically eliminating film slack and maintaining a state of tension of said film when the ink film cassette is being transported, and when the cassette is removed from the thermal transfer recording device while the ink film is being used or the like.